Organisms that can convert one or more monosaccharides into one or more biochemicals such as biofuels are well known. For example, both genetically modified (referred to as GM) yeast and non-genetically modified (referred to as non-GM) yeast are well known organisms that can convert sugars into alcohols such as ethanol and butanol via fermentation.
Often, such organisms are propagated by the manufacturer so as to produce a cell mass desired by a user, e.g., an ethanol manufacturer. However, many organisms are relatively quite expensive as compared to others. For example, many GM yeasts can be relatively much more expensive than non-GM yeasts. Thus, in some situations, it may be economically desirable for an ethanol manufacturer to purchase as little of a GM yeast as possible and then reproduce the yeast to provide a quantity sufficient for fermentation.
However, propagating yeast can be challenging. For example, some organisms such as Saccharomyces cerevisiae can be susceptible to the well-known “Crabtree effect” when grown on glucose, even under highly aerated conditions, if the glucose concentration in the medium is too high (e.g., exceeds 5 grams per Liter). If the glucose level becomes too high, the yeast can start to make ethanol through a fermentative pathway instead of producing more yeast through a respiration pathway (i.e., suppression of respiration by high levels of glucose). To help prevent the Crabtree effect, yeast manufacturers often grow yeast via a fed-batch or slow feeding process, where the carbon source (glucose) for producing yeast biomass is introduced at a rate that avoids undue ethanol production. However, fed-batch systems can be relatively expensive and challenging for ethanol manufacturers to control and manage.
There is a desire to develop methods of propagating organisms such as yeast using batch process protocols instead of fed-batch process protocols because batch processes can be relatively more simple to control and can be more tolerant to variation in process parameters (e.g., with respect to varying levels of a carbon source and the Crabtree effect).
Further, there is a desire to use alternative, more accessible, and/or more economical components used in a propagation medium (e.g., carbon source, nutrient source, and the like).